How do you know if it is a bent valve or if it is a sensor?

Hi,

A backfire is usually caused by excessive fuel entering the engine. Take a look through this link:

https://www.2carpros.com/articles/engine-backfires-while-running

Now, is the engine still running? As far as checking for a bent valve, the easiest thing to do is a compression test. If you have a bent valve, it will be stuck open and there will be little to no compression in that cylinder.

Here is a link that shows how it is done:

https://www.2carpros.com/articles/how-to-test-engine-compression

Let me know what you find or if you have other questions. Also, if you can record it cranking and upload it for me to hear, I should be able to tell you if there is a compression issue.

Take care,

Joe